This invention relates to a technology of erasing data stored in a storage system, in particular, to a technology of preventing a load for data erasure from being increased.
A storage area network (SAN) for coupling at least one external storage system and at least one computer is known. The SAN is particularly effective when a plurality of computers share a single large-scale storage system. A storage system including the SAN is excellent in scalability because such a storage system allows a storage system or a computer to be easily added or deleted.
As the external storage system coupled to the SAN, a disk array apparatus is frequently used in general. The disk array apparatus includes a large number of storage devices as represented by a hard disk (for example, magnetic storage devices) mounted therein.
The disk array apparatus manages a plurality of magnetic storage devices as a single redundant array of independent disks (RAID) group by a RAID technology. The RAID group forms at least one logical storage area. The computer coupled to the SAN executes data input/output processing for the logical storage area. When recording data on the storage area, the disk array apparatus records redundant data on the magnetic storage devices constituting the RAID group. Even if one of the magnetic storage devices is broken, the redundant data enables the recovery of the data.
In operation of the SAN, multiple types of storage systems different in categories or fabricated by different fabricators are sometimes present at the same time. In such a situation, the management such as capacity allocation and volume assignment should be carried out, taking account of the characteristics of each device. Therefore, a burden on an operation administrator is increased. In order to cope with such a problem, a virtual storage technology can be used. A storage virtualization device (virtual storage system) virtualizes a storage device mounted in another storage system as if the storage device were a resource stored on the storage virtualization device to provide the virtualized storage device for a host computer (see JP 2005-011277 A). Moreover, the virtual storage technology allows resources on different types of storage systems having different characteristics to be managed in an integrated fashion, thereby reducing the burden on the administrator.
Further, in order to erase the data recorded on the magnetic storage device, dummy data is written over the storage area from which the data is to be erased. However, if the dummy data is overwritten only once, there still exists remanent magnetism to allow the data to be recovered in some cases. In order to solve such a problem, processing of repeating the overwriting of dummy data for a plurality of times to completely eliminate the remanent magnetism is recommended. By completely eliminating the remanent magnetism to prevent the data from being recovered, a security risk can be lowered.